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In this article, the behavior of wood, plywood, and oriented strand board (OSB) under high- and low-velocity impact loadings was investigated experimentally. For the high-velocity impact test, limit velocity (Vbl) and impact energy absorbed (Eab) were determined by subjecting the material to different impact loading by conical nose projectile. For the low-velocity impact test, the materials were subjected to four levels of energy—10, 39, 78, and 98 J—and the time history responses of velocity, energy, load, and displacement were obtained. Additionally, quantitative data for damage size are presented. The results show that in comparison with OSB and solid wood plates, plywood presents better characteristics in response to both high- and low-velocity impact loadings.

The effects of variation in aluminium oxide nanoparticles in aluminium-based metal matrix composite on the compressive and sliding wear deformation have been investigated. The compressive and sliding wear resistance of the composite increase significantly with the addition of nanoparticles in the matrix. The 5% aluminium oxide nanoparticles in the composite were found to be the optimal weight fraction of added nanoparticles that produced higher static yield strength, hardness, scratch resistance and lower material loss in wear in the composite. The addition of nanoparticles, beyond 5% weight fraction, in the matrix showed adverse effects in the performance of the composite due to its higher brittleness. The effects on wear properties of the composite with added nanoparticles beyond optimal weight fraction were more detrimental than those with lower weight fraction of nanoparticles.

Metallic bone fixations, due to their high rigidity, can cause long-term complications. To alleviate metallic biomaterials’ drawbacks, in this research new Glass Fiber/Polypropylene (GF/PP) composite internal fixations were developed, and an investigation of their mechanical behavior was performed through in vitro biomechanical experiments. Short randomly oriented, long unidirectional prepreg, and long unidirectional fiber yarn were considered as reinforcements, and the effects on their mechanical properties of different manufacturing processes, that is, 3D printing and heat-compressing, were investigated. The constructed fixation plates were tested in the transversely fractured diaphysis of bovine tibia under axial compression loading. The overall stiffness and the Von Mises strain field of the fixation plates were obtained within stable and unstable fracture conditions. The samples were loaded until failure to determine their failure loads, strains, and mechanisms. Based on the results, the GF/PP composite fixation plates can provide adequate interfragmentary movement to amplify bone ossification, so they can provide proper support for bone healing. Moreover, their potential for stress shielding reduction and their load-bearing capacity suggest their merits in replacing traditional metallic plates.

The current study investigated the influence of incorporation of graphene nanoplatelets (GNPs) on quasi-static behavior of composite and fiber metal laminate (FML) panels. The unmodified and modified composite specimens and FML panels with 2/1 configuration were fabricated using a hand lay-up method and investigated through a quasi-static punch and indentation testing. The two sets of tests were conducted with a flat-ended indenter and the loading conditions were the same for all samples, except support spans which were varied. Following experimental testing, possible damages at the punch region were closely investigated and localized and global damages were observed. The results revealed that adding 0.2 wt% GNPs improved the strength and fracture toughness of specimens by delaying the failure modes. On the contrary, GNPs made the bonding between the aluminum and composite interface to weaken.

The human being has always been looking for optimal use of his surrounding materials and over the years, has managed to invent various structures with special properties. Lattice structures are widely used in various applications due to their lower weight and desirable compressive strength. An example of these structures is the honeycomb that is very popular and many studies have been done about it. A new type of lattice structures is auxetic structure that has negative Poisson’s ratio due to its geometry. This characteristic has caused auxetic structures to have unique properties such as high shear strength, indentation resistance and energy absorption. Investigation of energy absorption of auxetic structures is a subject that has not been studied in researches. In this study, the ability of some auxetic structure for absorbing energy is investigated at quasi-static and low velocity impact transverse loading. Specimens with three types of geometries (re-entrant, arrowhead and anti-tetra chiral) are fabricated using additive manufacturing method (3D printing). Discussion about energy absorption and failure mechanisms of all three structures were carried out and compared in both types of loading.

Mechanical properties and manufacturing processes of Glass Fiber/Polypropylene (GF/PP) composites for application of flexible internal long bone fracture fixation plates have been investigated. PP/Short Chopped Glass Fiber (PPSCGF), PP/Long Glass Fiber (PPLGF) and PP/Long Glass Fiber Yarn (PPLGFY) were used in fabrication of the fixation plates. The PPSCGF and PPLGF plates were made by the heat-compressing process and Three-dimensional (3D) printing method was used to make the PPLGFY ones. The values of Young’s modulus, tensile strength, flexural modulus and strength, and impact strength of the PPSCGF in the fiber longitudinal direction were found to be [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2, respectively. Where, these values for the PPLGF were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa, and [Formula: see text]kJ/m2 and for the PPLGFY were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2. These have been found to be in close agreement with the human bone properties. Furthermore, the strength and modulus values of the plates were reasonable to be used as a bone implant applicable for bone fracture reconstructions. Hence, the study concluded that the GF/PP composites are useful for load-bearing during daily activities and would be recommended as a choice in orthopedic fixation plate applications. It will help the researchers for development of new fixation designs and the clinicians for better patient’s therapy in future.

The employment of lightweight structures is one of the most important goals in various industries. The lightweight sandwich panel is an excellent energy absorber and also a perfect way for decreasing the risk of impact. In this paper, a numerical study of high-velocity impact on honeycomb sandwich panels reinforced with polymer foam was performed. The results of numerical simulation are compared with the experimental findings. The numerical modeling of high-velocity penetration process was carried out using nonlinear explicit finite-element code, LS-DYNA. The aluminum honeycomb structure, unfilled honeycomb sandwich panel, and the sandwich panels filled with three types of polyurethane foam (foam 1: 56.94, foam 2: 108.65, and foam 3: 137.13 kg/m3) were investigated to demonstrate damage modes, ballistic limit velocity, absorbed energy, and specific energy absorption (SEA) capacity. The numerical ballistic limit velocity of sandwich panels, filled with three types of foam, was more than that of a bare honeycomb core and unfilled sandwich panel. In addition, the numerical results showed that the sandwich panel filled with the highest density foam could increase the strength of sandwich panel and the numerical specific energy absorption of this structure was 23% more than that of unfilled. Finally, the numerical results were in good agreement with experimental findings.

The paper investigates the addition of Nano-Al2O3 powder (alumina, Average Particle Size: 20 nm) on the characteristics of the Medium Density Fibreboards (MDF) made by the forest fibers. Some impor...

This study proposes a new theoretical model for high-velocity impact in two kinds of targets, Kevlar/elastomer and Kevlar/epoxy composites, and comprehensively discusses and compares these. In this analysis, with the aid of hyperelasticity theory, energy absorption equations are derived based on the linear and nonlinear behavior of constituents to assess the dependence of the ballistic limit on the interaction of the first, second, third, and fourth layers of the laminate on each other. Furthermore, to investigate the matrix effect on the in-plane shear, tensile tests were performed at [Formula: see text] direction for both Kevlar/elastomer and Kevlar/epoxy composite laminates. The results indicate that the adhesion of Kevlar fibers to the rubber matrix is more substantial than their adhesion to the epoxy matrix, increasing the failure shear strain of elastomeric composites and reducing the debonding between the fiber and the matrix which led to greater ballistic velocity. The results of the experimental tests verified the proposed model and confirmed its precision. With this verified model, the thickness effect on the ballistic behavior of the targets was investigated.

Gradient distribution of vascular structure made the bamboo wall structure so effective which improved the load-bearing capacity of such bio-mimicked energy absorption structures and modify the crush behavior of thin-walled composite tubes. In this research, the influence of the layering design and stacking sequence on the crush behavior, failure mechanism and absorbed energy of bamboo-inspired GFRP composite tubes is assessed experimentally and numerically. Quasi-static compression tests were conducted to explore seven permutations of Coarse Woven (CW), Fine Woven (FW), and Unidirectional (UD) E/glass fiber sheets, taking into account the longitudinal vascular bundles strengthened by organic matrix. Samples were fabricated employing a modified hand laying up method by using mechanical pressure to obtain better surface finishing and interlaminar adhesion compared to conventional hand layering up methods. To evaluate the corresponding crashworthiness parameters and characterize the crushing behavior of composite tubes, quasi-static axial compressive loading was done. The numerical simulations were validated versus experiments by a commercial finite element (FE) LS-DYNA integrating material model 54. The predicted load-displacement curves and failure mechanisms of FE analysis demonstrate acceptable correlations with visual observations during experimentation. Furthermore, the parametric numerical was performed to examine the effect of different distributions of vascular bundles. The FE analysis results revealed that the crushing behavior of bio-inspired composite tubes depended substantially on layering configuration and the stacking sequence design. The outcomes showed that the combination of woven and unidirectional fibers, respectively, located in the inner layer and hoop direction provide the optimal layering configuration design in terms of crush length efficiency, crush load efficiency, Specific energy absorption, stable progressive crushing, and better manufacturing quality.

This paper presents an analytical model for the high-velocity impact behavior of autoclaved aerated concrete (AAC) blocks under flat-ended cylindrical projectile. This model employs an energy balance approach to derive the governing differential equations related to the process. The model considers four energy absorbing mechanisms including crushing, tensile fracture, plug kinetic, and friction loss. A closed-form solution was presented to the derived governing differential equations using singularity functions. Singularity functions were used to incorporate discontinuities due to various energy absorbing mechanisms. Results of the present model are reasonably in good agreement with presented experimental results. The effects of various impact parameters on the residual velocity and energy absorption were studied and the results are reported, discussed and commented upon.

This paper presents a comparison of behavior and energy absorption of neat Kevlar fabric and polymer matrix composites under high velocity impact loading . Two types of matrices including rubber and thermoset (epoxy) matrices were used in order to study the effect of a hard and brittle matrix compared with the soft and flexible matrix on energy absorption of the composite. Moreover, two types of rubber matrix with high hardness (HH) and low hardness (LH) were used in this study to investigate the effect of rubber matrix formulation on impact resistance of composites. Ballistic impact tests were performed by firing a 10 mm hemispherical projectile onto neat fabric and composites in a velocity range of 30–150 m/s for two- and four-layer samples. Results show that the matrix affects the ballistic performance of composites significantly. Rubber matrix enhances the energy absorption of the fabric by keeping composite flexibility. Increase the number of layers for Kevlar/rubber composite results in better ballistic performance. On the contrary, the thermoset matrix leads to an inflexible composite that restricts the fabric deformation and has a negative effect on the fabric’s ballistic performance. Finally, damage mechanisms were discussed in detail for each sample.

This study aims to investigate the quasi-static and high strain rate deformation of an aluminum-based metal matrix composite reinforced with Al2O3 nanoparticles. The addition of Al2O3 nanoparticles with an optimal weight percentage increased the strength and energy absorption capacity of the composite material. The deformation characteristics of the material were found to be strain rate sensitive. It was concluded that the usage of an optimal weight percentage of nanoparticles results in a markedly higher energy absorption capacity in a variety of strain rates of deformation. Moreover, the energy absorption capacity of the present metal matrix composites increased significantly at the higher strain rates of deformation. It was found that the excessive addition of nanoparticles to the metal matrix decreases the energy absorption capacity as well as strain rate sensitivity of the composite material.

This article presents a novel general theory to estimate total absorbed energy (TAE) by two main absorber mechanisms: bending and plastic line. Furthermore, as case studies, some theoretical formulas are derived for predicting TAE of circular metal tubes during lateral flattening and indentation processes, based on three different material models of Rigid-perfectly plastic, Rigid-linear work hardening and Power hardening. Furthermore, some indentation and flattening tests are carried out on circular brazen and aluminum tubes to investigate correctness and accuracy of the derived theories. In the theoretical part, theoretical equations are derived for both thick-walled and thin-walled structures; and a multi criteria equation is derived to estimate TAE of two main energy absorbing mechanisms involving bending and plastic hinge line; and, then, based on the derived general formulas, some theoretical relations are calculated to predict TAE of indentation and flattening processes, as case studies. In the indentation process, circular tubes are considered between a slab rigid indenter and a rigid platen; and in the flattening process, circular tubes are laterally compressed between two rigid platens. To verify the derived equations, various experiments are performed on some circular brazen and aluminum specimens that are laterally indented and flattened in the quasi-static condition. In the indentation tests, different tubular samples with various wall thicknesses and radii of cross–section and material types are loaded under different slab rigid indenters with different widths. Then theoretical estimations of TAE by circular tubes during the indentation and flattening processes are compared with the corresponding experimental results. Also, effects of tube wall thickness and indenter width are investigated on TAE of tubes, experimentally and theoretically. Performed investigations illustrate that by increasing the wall thickness and indenter width, TAE of indented tubes increases. Also, the present research work affirms that TAE by circular tubes through the flattening process is higher than the corresponding value of their indentation process, theoretically; and upper limit of TAE of circular tubes through the indentation process occurs when, width of slab indenter reaches to half of tube initial perimeter.

The present study is devoted to investigating the mechanical characteristics of a novel natural rubber (NR)-based elastomer nanocomposite reinforced with carbon black and alumina nanoparticles acting as partial and primary reinforcements, respectively. Before conducting various mechanical tests on the specimens, the vulcanization properties of this elastomer nanocomposite was surveyed. It is demonstrated that adding the alumina nanoparticles to the NR-based elastomer matrix can significantly reduce the cure time and improve the quality of the vulcanizates. Then, the influence of alumina nanoparticles on the modulus, tensile strength, elongation at break, and energy absorption capacity of the elastomer nanocomposite were assessed, and the ideal nanoparticles’ weight percentage was determined to be 10%. This is supported by calculating the Reinforcing Efficiency Parameter (REP), indicating that the elastomer nanocomposite with 10% alumina has the best reinforcing efficiency in tensile properties. Also, using the Split Hopkinson Pressure Bar (SHPB), it was found that the material is exceptionally strain-rate sensitive, and the specimens exhibited much higher values of stiffness and energy absorption under high strain-rate loading. It is inferred from the results that the elastomer nanocomposite reinforced with the optimal amount of alumina nanoparticles can be an excellent candidate for energy absorption applications under high strain-rate loadings.

One of the best nondestructive techniques to evaluate the buckling behavior of imperfection-sensitive structures is the vibration correlation technique (VCT). This paper presents an analytical formulation for the free vibration of axially loaded composite lattice sandwich cylinders (CLSC) and numerical and experimental validations of the VCT applied to such structures. From an analytical point of view, the equations are obtained through the Rayleigh-Ritz method considering first-order shear deformation theory (FSDT). For the numerical verification of the VCT, three types of linear and nonlinear finite element analyses are performed. At first, numerical results for the critical buckling load and the first natural frequency at different load levels are compared with the corresponding analytical ones, validating the numerical models. Then, the numerical models are extended considering geometric nonlinearities and imperfection to simulate the variation of the first natural frequency of vibration with the applied load. As well, a nonlinear buckling analysis is also performed using the Riks method for a better comparison of the VCT results. In the last section, four specimens are fabricated using a new rubber mold and a filament winding machine. Additionally, the experimental buckling test is carried out, verifying the results of the VCT approach. The results demonstrate that the maximum difference between the estimated buckling load using the VCT approach and the corresponding nonlinear and experimental buckling loads is less than 5%, being the VCT result more accurate than the numerical one. Moreover, the proposed VCT provided a good estimation of the buckling load of the CLSC, considering a maximum load level of at least 62.1% of the experimental buckling load.

This paper aims to investigate the performance of an aluminum–rubber composite plate under impact loading. The impact resistance of the plate has been evaluated using both experimental and numerical methods. The experimental tests were carried out using gas gun at velocities of 75, 101, 144 and 168 m/s. The energy absorption of composite plates has been closely examined for all samples. The effect of rubber layer positioning either on front face or on back face of the aluminum plate was also evaluated. It was found that the composite plate with rubber on front face provides higher performance to absorb the energy. In parallel to the experiment, a finite element model was created using the finite element software LS-DYNA to simulate the response of the aluminum–rubber composite plate under a high energy rate loading condition. The data obtained from finite element modeling shown a close agreement with the experimental results in terms of failure mechanism and energy absorption. In addition, a parametric study was carried out incorporating different impact velocities, rubber formulation, rubber layer thickness, interface bonding strength between rubber and aluminum layers and ballistic performance of aluminum-rubber sandwich panel. It was concluded that by increasing the rubber layer's thickness the energy absorption of the composite plate will be increased, especially when rubber layer placed in front face of the aluminum plate. Although at high interface bonding of rubber and aluminum layer, the composite with rubber layer in front face has better performance, but low bonding of interface lead to higher energy absorption in back face configuration.

This study presents the response of rubber panels subjected to high-velocity impact loading. The mechanical properties and impact performance of rubber panels are altered by the variation in compound ingredients. To investigate the effect of compound ingredients, two types of rubber panels with high (SHA70) and low hardnesses (SHA45) were prepared, and mechanical properties and impact resistance of the panels were measured by high-velocity impact tests in a velocity range of 70–160 m/s. Ballistic limits of about 80 and 94 m/s were obtained for the low- and high-hardness rubbers, respectively, which show that the energy absorption of rubber panels increases as filler loading content increases. In this respect, the finite-element simulation has been performed to investigate the ballistic performance of rubber panels numerically. Rubber panel has been modeled using the LS-DYNA software and employing the experimental results of tensile test to characterize the behavior of panel. The findings show a good agreement between the numerical and experimental data. To study the effect of projectile’s shape, impact resistance of the rubber panels against hemispherical projectiles with different length-to-diameter (L/D) ratios (projectiles with diameters of 8, 10, and 12 mm) was measured and the model was also used. The results demonstrate that energy absorption of the panel increases as the diameter of projectile increases. The energy absorbed by the rubber panels appears in the form of damages that lead to increase their damage zone.

In this article, the quasistatic penetration tests were investigated on unfilled and polyurethane foam filled honeycomb sandwich panels. Failure mechanisms, specific energy absorption, interaction ...

This paper investigates the eccentric low-velocity impact of Fiber metal laminates (FMLs) subjected to spherical projectile using a unified Zig-Zag plate theory. The presented zig-zag plate theory enforces transverse shear stress continuity through the thickness and can be reduced to conventional plate theories using appropriate shape function. The governing equations and suitable boundary conditions are obtained using the principle of minimum total potenital energy . Runge-Kutta method is employed to solve initial value problem resulted by the method of Ritz. The present model is validated by comparison and good agreement between its results and those of reports in open literature. Influence of various specifications of impact phenomenon such as laminate thickness , projectile radius, projectile velocity , in-plane load and eccentricity parameter is examined on deflection and contact force time history. The obtained results indicate that continuity of transverse shear stress is required to achieve accurate contact force even for moderately thin FMLs.

In this study, two computationally efficient and accurate solution methods for heat transfer analysis in composite metal cylindrical vessel subjected to internal thermal load are presented. In order to accurately account for the thickness effects, the layerwise theory is employed to approximate the temperature field. In the first solution method, differential quadrature method (DQM) is implemented to discretize the resulting equations in the both spatial and time domains. In the second approach, DQM is applied to discretize equations in the axial direction while Newmark's time integration scheme is used to solve the problem in the time domain. The fast convergence rate of the methods is demonstrated and their accuracy is verified by comparing the results with those obtained using ABAQUS software and also with the exact solutions. Less computational efforts of the proposed approaches with respect to the finite element method is observed. Furthermore, comparative studies are performed and it is found that layerwise theory provides the capability of precise modeling of laminated composite shells.

The main aim of the present research is to investigate the quasi-static penetration process of cylindrical indenters with different nose shapes into multilayered composite panels made of Dyneema and Glass woven fibers, and aluminum face sheets. For better understanding of the perforation mechanism of the composite panels, effects of indenter geometry, stacking sequences, and boundary conditions are studied and their effects on energy absorption, specific absorbed energy, maximum deformation, peak load, and failure modes are evaluated and discussed. Samples with different layering configurations loaded under quasi-static punch and indentation with loading rate of 5 mm/min using universal testing machine and cylindrical rigid indenters with different nose shapes geometries consist of blunt, hemispherical, conical, and ogival. Regarding the boundary condition effects, two different rigid fixtures are designed and manufactured with the same external square perimeter (250 × 250 mm) and two different internal perimeters of circular and square shapes respectively, with diameter of 15 mm and edge side of 100 mm. Results show that the hybrid composite panels composed of Dyneema sheets, exhibits significantly better load carrying capacity and specific absorbed energy under both loading conditions. Indenter nose shape significantly affects elastic load, peak load, and energy absorption and maximum deformation. Furthermore, from visual observations based on digital microscopic images, fiber breakage, fiber pull out, intralaminar delamination, and debonding between the composite layers within the damage zone were inspected and recognized as the main damage mechanisms of panels. Output data obtained from all the experimental investigation were reported, discussed, and commented upon.

In the present study, static behavior of short hybrid laminate beams was investigated using a unified zig-zag theory (ZZT) containing various beam theories as special cases. This theory satisfies transverse shear stresses continuity in the interface of layers via piece-wise continuous arbitrary shape functions. The principle of virtual work was employed to derive unified equilibrium equations and suitable boundary conditions. The present theory obviates the need for stress recovery for continuous transverse stresses. A general solution was presented to analyse high transversely anisotropic laminates under several kinds of transverse loads (general lateral, sinusoidal and point load) and non-linear thermal loads. The validity of this model is demonstrated by comparison of its predictions and good agreement with published results in literature. Numerical examples were given to investigate the impact of the transverse anisotropy on displacement, strain and stress fields through the thickness. The results show that the piece-wise continuous exponential and sinusoidal shape functions provide more accurate transverse stress distribution in comparison with other shape functions. In addition, the results show that the continuity of transverse shear stress through the thickness plays an important role in analysing transversely anisotropic laminated beams. A comparison of present ZZT and existing exact elasticity solutions shows that the current theory is simple and efficient.

In this work nanopolyurea is used as reinforcement for curved steel plates under low velocity impact loading. Experimental and numerical analysis are used to study the effect of plate curva...

In this paper, experimental studies of impact loading on honeycomb sandwich panels filled with polymer foam were investigated. The structural elements used in this research were aluminium plate, al...

In this study, thermoelastic stress analysis in composite metal cylindrical vessel is investigated with the help of two theories, first-order shear deformation theory (FSDT) and layerwise theory, using differential quadrature method (DQM). Hamilton principle and FSDT are employed for derivation of the principle differential equations. DQM and Newmark’s methods are used for stress analysis of a composite metal cylindrical vessel subjected to internal dynamic pressure and thermal load achieved from experimental test. In order to more accurately estimate the thickness effect, the layerwise theory is applied to approximate the temperature field. In this solution method, DQM is used to discretize the resulted governing equations while Newmark’s method is implemented to solve the problem in the time domain. It was observed that the fast convergence rate of the DQM method and its accuracy is confirmed by comparing the results with those obtained using ABAQUS software and also with the exact solutions. Furthermore, it was achieved significantly less computational efforts of the proposed approaches with respect to the finite element method.

Sandwich tube structures bio-mimicking horsetail and human tendons offered significant improvement over traditional single and multi-cell tubular energy absorbers. The present research aims to investigate three manufactured hybrid multi-cell aluminum and GFRP sandwich tubes subjected to quasi-static and low-velocity axial compression . The crashworthiness characteristics and axial crushing failure mechanisms of sandwich tubes are discussed and compared with the quasi-static axial behavior of single Al and GFRP tubes. Further investigations, based on the validation of an FE model versus experimental results, using the commercial finite element code LS-DYNA, on the effects of material permutation and inner tubes diameter are perceived through the full-factorial approach of FE parametric study . The quasi-static results revealed that, packing the Al and GFRP tubes in the form of multi-cell sandwich tube generally improves the crushing patterns of individual hollow tubes. Moreover, the low-velocity response of the hybrid multi-cell sandwich tubes showed that the crushing response of the GFRP components despite AL ones depends significantly on the strain rate , where Al tubes undergo irregular diamond deformation. Eventually the results of bio-inspired hybrid multi-cell sandwich tubes indicate that incorporating more GFRP tubes provided an optimal crashworthy design and conduce to a broad range of applications within aerospace, transportation.

In this study, experimental investigations are implemented to evaluate the effect of incorporation of graphene nanoplatelets (GNPs) on the low-velocity impact behavior of composites and fiber metal laminates (FMLs). The hand layup technique is employed to fabricate composite specimens and FML panels with 2/1 configuration. Impact response and damage patterns of unmodified and modified specimens subjected to various impact energy levels are compared. The results reveal that the incorporating 0.2 wt% of GNPs strengthens the impact resistance of FMLs so that the modified panels possess higher bending stiffness, peak load, energy absorption and SEA compared to the unreinforced ones. Visual inspections and SEM images exhibit that the inclusion of GNPs enhances the adhesion between resin/fibers as well as composite plies, thereby reducing damage area and increasing penetration threshold of FMLs. In addition, reinforcing composite panels considerably improves the impact behavior in comparison with the unmodified composites.

The main focus of this review is on soft composites, relatively new to the literature. The ballistic fabrics, mechanism of ballistic energy absorption and parameters affect the ballistic performance of fabrics are reviewed. Adding shear thickening fluid (STF) and natural rubber (NR) to fabric and their potential to enhance the impact performance of woven fabrics are considered. Shear thickening mechanism, parameters influence the Shear thickening and impact response of fabric/STF composite are explored. Numerical modelling techniques for the estimation of impact resistance of fabric/STF are outlined. Also the role of shear thickening fluid in energy absorption of fabric/STF composite was investigated. Moreover mechanical and impact characteristics of elastomeric composites which contain one rubbery part as either matrix or completely separate media are explored as well, which have not been considered within previous review papers so far.

Effect of adding carboxyl-modified multi-walled carbon nanotubes (COOH-MWCNTs) on the high velocity impact of sandwich panels with plywood core and two different facesheets, E-glass/epoxy and E-glass/ nylon 6, was investigated in this study. Facesheets were prepared with and without COOH-MWCNTs. Three different weight percentages of 0.3, 0.5, and 1 wt% of COOH-MWCNTs were used to reinforce epoxy and nylon 6 polymers. The sandwich panels’ estimated ballistic limit ( Vbl) and impact energy absorbed ( Eab) were determined by subjecting them to impact velocities in their ballistic limit range and above by conical nose projectile. It was found that the sandwich panels containing E-glass/ epoxy facesheets exhibited more energy absorption than those containing E-glass/nylon 6 facesheets. Moreover, the high velocity impact response of sandwich panels improved with the increase of COOH-MWCNT content. Besides, the damage area for different types of materials studied is presented, and it is observed that at a given impact velocity, the damage size on the rear facesheet of target around the point of impact decreases on addition of COOH-MWCNTs.

In this article, absorbed energy per unit of initial tube length, initial peak force and mean folding force in empty and polyurethane foam-filled simple and grooved specimens with circular cross section are investigated, experimentally. Results demonstrate that in the empty and foam-filled simple specimens, absorbed energy per unit of initial tube length, initial peak force and mean folding force are larger than the corresponding values of the empty and foam-filled grooved specimens, respectively. But, increment of absorbed energy due to the foam-filler in the grooved tubes is more than the corresponding value in the simple specimens. Also, diagrams of absorbed energy and folding force versus the grooves distance have the minimum value. Therefore, there is a critical value for the grooves distance and according to the application viewpoint, to produce a good energy absorber, the grooves distance is selected far from the critical grooves distance. The experimental results show that when the grooves distance (λ) decreases, deformation mode inclines to the concertina (regular) mode and when λ increases, the deformation mode inclines to the diamond mode. Finally, a semiempirical relation is derived to predict the initial peak force of empty and foam-filled grooved tubes.

This study presents the high-velocity impact performance of a composite material composed of woven Kevlar fabric impregnated with a colloidal shear thickening fluids (STFs). Although the precise role of the STF in the high-velocity defeat, process is not exactly known but it is suspected to be due to the increased frictional interaction between yarns in impregnated fabrics. In order to explore the mechanism of this enhanced energy absorption, high-velocity impact test was conducted on neat, impregnated fabric and also on pure STF without fabric. A finite element model has been carried out to consider the effect of STF impregnation on the ballistic performance. For this purpose, fabric was modeled using LS-DYNA by employing the experimental results of yarn pull-out tests to characterize the frictional behavior of the STF impregnated fabric. The simulation result is a proof that the increased performance for STF impregnated Kevlar fabric is due to the increased friction.

In this paper, the penetration performance of shaped charge in tandem warhead with different liner materials into thick concrete targets is investigated. For this purpose, the penetration process and the damage mechanism of concrete target by shaped charges with two different liner materials are analyzed by experimental and numerical methods. The used materials for two liners are aluminum and copper. Comparison between experimental and numerical results is in good agreement with each other. The obtained results suggest that both types of shaped charge are capable of destroying thick concrete targets, but aluminum conical liner has more significant effect in creating penetration depth, tunnel diameter rather than copper conical liner. Also, the shaped charge with aluminum conical liner develops very large spalling and scabbing area in the front and back of the concrete target. Hence a shaped charge with aluminum material liner is quite suitable for forward projectile of tandem warhead.